<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <script>
        var year=prompt("请输入年份")
        var a1=year%4==0;
        var a2=year$100=0;
        var a3=year%400==0;
        var shuru=(a1&&a2)||a3;
        if(shuru=true){
            alert("是闰年");
        }else if(shuru=false){
            alert("是平年");
        }
        
        
    </script>
</body>
</html>